Articles of footwear generally include two primary elements, an upper and a sole structure. The upper is formed from a variety of material elements (e.g., textiles, foam, leather, and synthetic leather) that are stitched or adhesively bonded together to form a void on the interior of the footwear for comfortably and securely receiving a foot. More particularly, the upper generally extends over the instep and toe areas of the foot, along the medial and lateral sides of the foot, under the foot, and around the heel area of the foot. In some articles of footwear, such as basketball footwear and boots, the upper may extend upward and around the ankle to provide support or protection for the ankle. Access to the void on the interior of the upper is generally provided by an ankle opening in a heel region of the footwear. A lacing system is often incorporated into the upper to adjust the fit of the upper, thereby permitting entry and removal of the foot from the void within the upper. The lacing system also permits the wearer to modify certain dimensions of the upper, particularly girth, to accommodate feet with varying dimensions. In addition, the upper may include a tongue that extends under the lacing system to enhance adjustability of the footwear.
The sole structure is located adjacent to a lower portion of the upper and is generally positioned between the foot and the ground. In many articles of footwear, including athletic footwear, the sole structure conventionally incorporates a sockliner, a midsole, and an outsole. The sockliner is a thin compressible member located within the void and adjacent to a lower surface of the void to enhance footwear comfort. The midsole, which is be secured to a lower area of the upper and extends downward from the upper, forms a middle layer of the sole structure. In addition to attenuating ground reaction forces (i.e., providing cushioning for the foot), the midsole may limit foot motions or impart stability, for example. The outsole, which may be secured to a lower surface of the midsole, forms the ground-contacting portion of the footwear and is usually fashioned from a durable and wear-resistant material that includes texturing to improve traction.
A variety of conventional midsoles incorporate a fluid-filled chamber that increases durability of the footwear and further enhances the attenuation of ground reaction forces in the sole structure. In some footwear configurations, the fluid-filled chamber may be at least partially encapsulated within a polymer foam material. In other footwear configurations, the fluid-filled chamber may substantially replace the polymer foam material. That is, substantially all of the midsole or a majority of the midsole may be formed from the fluid-filled chamber. In general, fluid-filled chambers are formed from a polymer material that is sealed and pressurized, but may also be substantially unpressurized or pressurized by an external source. In some configurations, textile or foam members may be located within the chamber, or reinforcing structures may be bonded to an exterior surface of the chamber to impart shape to or retain an intended shape of the chamber.
Fluid-filled chambers may be manufactured through various processes, including a two-film technique, thermoforming, and blowmolding. In the two-film technique, two planar sheets of polymer material are bonded together in various locations to form the chamber. In order to pressurize the chamber, a nozzle or needle connected to a fluid pressure source is inserted into a fill inlet formed in the chamber. Following pressurization, the fill inlet is sealed and the nozzle is removed. Thermoforming is similar to the two-film technique, but utilizes a heated mold that forms or otherwise shapes the sheets of polymer material during the manufacturing process. In blowmolding, a molten or otherwise softened elastomeric material in the shape of a tube (i.e., a parison) is placed in a mold having the desired overall shape and configuration of the chamber. The mold has an opening at one location through which pressurized air is provided. The pressurized air induces the liquefied elastomeric material to conform to the shape of the inner surfaces of the mold, thereby forming the chamber, which may then be pressurized.
Although fluid-filled chambers may be utilized in footwear, various configurations of the fluid-filled chambers may also be utilized in other products. For example, fluid-filled chambers may be incorporated into backpack straps, golf clubs, and cushions.